The invention is directed to a transparent casting resin compound for casting out optoelectronic components.
Opto-electronic components must be protected against adverse environmental influences to be functionally reliable and to have dependable utilization with up to 100,000 operating hours. Due to advantageous thermal-mechanical as well as electrical characteristic, high-purity epoxy resins are often utilized in electrical engineering and electronics. Epoxy resins have an extraordinarily high chemical stability for plastics and are therefore employed for the encapsulation of light-emitting diodes (LEDs) at operating temperatures of currently up to 110° C. The transparent and non-yellowing duromer materials exhibit glass transition temperatures of usually up to 120° C. With increasing power density and integration density in the field of opto-electronics, crack-resistant, highly loadable compounds of epoxy resin shaped materials having glass transition temperatures of above 130° C. are demanded. In addition to increased operating temperatures, the quality standards must be qualified under aggravated temperature cycles and temperature shock conditions for innovative LED applications in the automotive sector. The encapsulation materials must be completely cured in any case in order to avoid electrical degradation of the component during operation.
The epoxy casting resin shaped materials disclosed by DE 2642465 composed of cycloaliphatic casting resin mixtures with epoxies of the glycidylether type exhibit high glass transition temperatures>130° C. but appear unsuitable for fabrication use because of possibly excessively high health risks. Toxilogical investigations, which were made by leading institutions of these resin mixtures, yielded a substantiated suspicion of pronounced carcinogenic potential in this context.
DE 32 41 767 A1 discloses a colored casting compound on the basis of cycloaliphatic and aromatic epoxies and carboxylic acid anhydride hardening agents are known that are distinguished by their good color stability and that are proposed for optical applications.
SMD-LEDs are currently encapsulated with two-component, thermally cross-linking reaction resins on a basis of anhydride-epoxy casting resin. The optimized rheological and thermally reactive properties of the casting compound allow cost-efficient mass production processes. The epoxy resin component is composed of a moderately viscous bisphenol-A-diglycidylether with reactive epoxy diluent, and anti-foaming mixture as well as a pigment batch that enables transparent shaped materials after the hardening step. This A-component can be laced further with low-molecular alcohols. Pigments that can be distributed with molecular dispersion are utilized for pigmentation. Diffusely light-emitting components are utilized by adding specific diffuser pastes on the basis of inorganic pigments. Different zinc-salt accelerated anhydrides are modified with acidic ester upon addition of oxidation stabilizers for the hardener component. With existing casting compound, the increase in quality features of future LED generations, however, cannot be adequately satisfied in view of a temperature range of utilization and a thermal fatigue resistance according to automotive standards.